Foraging behaviour of South American fur seals Arctocephalus australis: extracting fine scale foraging behaviour from satellite tracks

Abstract

Industrial exploitation of marine resources may adversely affect marine top predators, but protecting important foraging areas may reduce impacts. Such areas may be relatively small and discrete, and anthropogenic disturbance effects may also be geographically or temporally localised. Avoiding overlap may be simple and inexpensive, but requires accurate, fine-resolution data on habi- tat use. Here we report the results of a satellite telemetry-based study of foraging behaviour of South American fur seals in relation to proposed offshore oil exploration areas in Falkland waters. We developed a simple track-smoothing algorithm incorporating estimated location error and temporal distribution of position fixes and used the temporal frequency distribution of received transmissions to infer haulout events and further constrain the tracking data. The accuracy of smoothed data was tested against independently derived foraging-trip data and then used to describe foraging behav- iour of 14 fur seals between October 1999 and September 2000 and demonstrate a dramatic seasonal pattern in foraging locations. Early in lactation, all seals made short-duration, nocturnal foraging trips, and foraging was restricted to a small area within 20 km of the breeding site. By late summer, trips were over 6 d long and ranged over 195 km from the island. Overall, 15 to 20% of late lactation- phase foraging occurred in the oil exploration zone. Restricted foraging ranges early in lactation reduced the likelihood of interactions with offshore activities. Counterintuitively offshore activities may be less disturbing when pups are young.